SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 59,968	$ 10,283
Accounts receivable	313,576	266,426
Income tax receivable	6,792	21,727
Other current assets	76,627	61,958
Total current assets	1,198,319	1,030,030
Investments and other assets
Other assets	92,922	96,953
Total investments and other assets	1,485,866	1,352,823
Total Assets	20,020,421	18,479,247
Current liabilities
Accounts payable	318,585	346,448
Accrued taxes	159,551	144,899
Common dividends payable	93,531	87,982
Short-term borrowings	169,000	114,675
Current maturities of long-term debt	0	800,000
Operating lease liabilities	74,785	12,713
Other current liabilities	187,448	168,323
Total current liabilities	1,360,433	2,078,365
Deferred credits and other
LONG-TERM DEBT LESS CURRENT MATURITIES (Note 7)	6,314,266	4,832,558
Operating lease liabilities	361,336	51,872
Other	190,643	159,844
Total deferred credits and other	6,592,929	6,015,136
COMMITMENTS AND CONTINGENCIES (SEE NOTES)
Common stock equity
Common stock	2,677,482	2,659,561
Accumulated other comprehensive loss	(62,796)	(57,096)
Retained earnings	3,025,106	2,837,610
Total shareholders’ equity	5,633,503	5,430,648
Noncontrolling interests (Note 18)	119,290	122,540
Total equity	5,752,793	5,553,188	$ 5,348,705	$ 5,135,730
Total Liabilities and Equity	20,020,421	18,479,247
Pinnacle West
Current assets
Cash and cash equivalents	19	19
Accounts receivable	123,980	104,640
Income tax receivable	14,719	15,905
Other current assets	298	401
Total current assets	139,016	120,965
Investments and other assets
Investments in subsidiaries	6,400,339	6,067,957
Deferred income taxes	7,589	40,757
Other assets	52,595	50,139
Total investments and other assets	6,460,523	6,158,853
Total Assets	6,599,539	6,279,818
Current liabilities
Accounts payable	5,669	7,634
Accrued taxes	16,998	8,573
Common dividends payable	93,531	87,982
Short-term borrowings	169,000	114,675
Current maturities of long-term debt	0	450,000
Operating lease liabilities	90	81
Other current liabilities	15,306	15,126
Total current liabilities	300,594	684,071
Deferred credits and other
LONG-TERM DEBT LESS CURRENT MATURITIES (Note 7)	496,321	(575)
Pension liabilities	17,541	17,942
Operating lease liabilities	1,683	1,780
Other	30,607	23,412
Total deferred credits and other	49,831	43,134
COMMITMENTS AND CONTINGENCIES (SEE NOTES)
Common stock equity
Common stock	2,671,193	2,650,134
Accumulated other comprehensive loss	(62,796)	(57,096)
Retained earnings	3,025,106	2,837,610
Total shareholders’ equity	5,633,503	5,430,648
Noncontrolling interests (Note 18)	119,290	122,540
Total equity	5,752,793	5,553,188
Total Liabilities and Equity	$ 6,599,539	$ 6,279,818